Hydraulic locking device



Jan. 26, 1960 P. PORTER 2,922,497

HYDRAULIC LOCKING DEVICE Filed Nov. 19, 1956 3 Sheets-Sheet 1 w 4 M /Wvw Mw mm wm. waf wh,

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Jan. 26, 1960 P, L, PORTER 2,922,497

HYDRAULIC LOCKING DEVICE Filed Nov. 19, 1956 3 Sheets-Sheet 2' i5 fa 3Sheets-Sheet 3 Filed Nov. 19, 1956 some because the adjustment iscritical.

HYDRAULIC LOCKING DEVICE Percy Lee Porter, Los Angeles, Calif., assignerto P. L. Porter Co., Los Angeles, Calif.

Application November 19, i956, Serial No. 623,192

14 Claims. (Cl. 18S-96) This invention relates to a hydraulic lockingdevice that is adapted to extend and contract to hold two relativelymovable members at selected positions with respect to each other.

A hydraulic locking device of the type to which the invention pertainscomprises a cylinder coniining a quantity of hydraulic uid and a pistondividing the cylinder into two hydraulic chambers What may be termed alocking valve controls communication between the two chambers and isnormally closed to immobilize the piston. Space is also provided tofunction as a reservoir in communication with at least one of the twohydraulic chambers to hold a reserve supply of the Huid, the reservoirbeing adapted to expand and contract to accommodate thermal expansionand contraction of the fluid in the two hydraulic chambers.

A device of this type is disclosed in the Porter et al. Patent2,559,047, issued July 3, 1951, and the application of such a device tothe control of a tiltable back rest of a reclining chair is set forth inthe Armstrong Patent 2,522,246, issued September l2, 1950. These twoprior disclosures are hereby incorporated into the present disclosure byreference.

The ptupose of the present invention is lto provide special featuresthat meet certain problems and diiculties that arise in the installationand operation of a hydraulic locking device of this character. Thesefeatures have special utility in locking devices that are incorporatedin the construction of reclining chairs for use on passenger airplanes.A locking device for this special purpose is selected for the presentdisclosure and will provide adequate guidance for those skilled in theart who may have occasion to apply the same principles to other specificpurposes.

One of the problems to which the invention is directed is to providecorrect adjustment of the valve-operating mechanism. This problem hasbeen especially trouble- The valve-releasing mechanism on a typicalairplane reclining chair is actuated by a push button having a range ofmovement of only 3A; inch. A certain amount of lost motion is necessaryto make sure that the locking valve is permitted to close fully when thepush button is relaxed. Less than Ve inch of movement is available,then, to actuate the locking valve.

The heretofore prevailing type of locking device, such as described inthe above mentioned Porter patent, incorporates a valve-actuating memberin the form of a screw extending longitudinally into one end of thedevice and it is necessary to make the actual final adjustment of thisactuating screw when the locking device is installed in the recliningchair. As will be explained, the present invention provides a lbuilt-incam mechanism that may be accurately adjusted at the factory bench. Thisfeature not only simplifies the subsequent installation operation, butalso assures expert adjustment of the actuating mechanism.

Another problem arises from the fact that, in` some 2,922,497 PatentedJan. 26, 1960 instances where a relatively great operating force isavailable for the valve opening operation, it is desirable to providesubstantial operating resistance on the part of the 'valve mechanism;whereas, in other instances, the available operating force is relativelyweak and much weaker operating resistance should be provided. Theinvention meets this problem by providing both a valve spring and abooster spring to resist the operating force and by providing a simpleoptional spacer that may be inserted to cut 'olf the pressure from thebooster spring in those installations Where a relatively weak operatingforce is available. In this regard, a further feature of the preferredpractice of the invention is that the booster spring is present in themechanism primarily for an entirely diiferent purpose, its primaryfunction being to keep the reserve supply of liquid under adequatepressure.

Still another problem is to provide a degree of communication into andout of the hydraulic reservoir that is adequate for compensating flowwhen the fluid in the system expands and contracts thermally and yetprevents excessive fluid displacement into the reservoir Whenever anunusual pressure rise occurs in the hydraulic system. Such an unusualpressure rise may occur, for example, when the hydraulic locking deviceis subjected to an overriding mechanical pressure in the direction toopen the locking valve. This problem is solved by providing theequivalent of a check valve to oppose tiuid displacement into thereservoir and by further providing a suitable restricted bypass orbleeder passage for iiuid flow independently of the check valve.

A further dificulty that has been encountered is the development ofleakage through the locking valve. It has been found that such leakagecommonly arises from uneven spring pressure against the valve ball, theuneven pressure permitting erosion of the valve seat to occur. As willbe explained, this dihculty is solved by interposing what may be termeda floating ball guide between the valve ball and the spring.

A further feature of the invention is that it permits the whole lockingvalve assembly to be replaced without the necessity of dismantling thewhole structure. For this purpose, the piston that separates the twohydraulic chambers is mounted on a hollow piston rod that is open atboth ends. The locking valve seat is in the form of a removable insertthat is accessible for replacement through one end of the hollow pistonrod. The valve ball, ball guide, valve spring and spring follower areaccessible for replacement through the other end of the hollow pistonrod. In addition, the spring follower is accessible for adjustment topermit the pressure of the valve spring to be varied.

The various features and advantages of the invention may be understoodfrom the following detailed description considered with the accompanyingdrawings.

In the drawings, which are to be regarded as merely illustrative Fig. 1is a longitudinal sectional view of the presently preferred embodimentof the invention as designed for control of the back rest of a recliningairplane seat;

Fig. 2 is a greatly enlarged fragment of Fig. l, showing theconstruction of the locking valve, the locking valve being shown in itsnormal closed position;

Fig. 3 is a similar sectional View showing how the locking valve opensand the check valve closes in response to an overriding pressure;

Fig. 4 is a perspective view of the push rod that opens the valve;

Fig. 5 is a greatly enlarged fragmentary sectional view showing how thepush rod opens the locking valve;

Fig. 6 is a fragmentary, longitudinal sectional view showing how aspacer member may be inserted to isolate asaaes'/ the pressure of thereservoir spring from the valve-actuating mechanism. This view alsoshows the valve-opening cam mechanism in its normal inoperativeposition; and

Fig. 7 is a fragmentary view similar to Fig. 6, showing the cammechanism in its operating position.

The principal parts of the embodiment of the invention shown in Fig. linclude a cylinder 1t) and a piston assembly inside the cylinder, thepiston assembly comprising a piston 12 on a tubular piston rod 14 thatextends outward through both ends of the cylinder. The piston 12 isprovided with a suitable 0-ring 13. One end wall of the cylinder isformed by a bushing 15 which is provided with O-rings 16 and 17 forsealing contact with the tubular piston rod 14. This end wall may beintegral with the cylinder 10, if desired.

The other end wall of the cylinder 10 is provided by a threaded boss 18of a tubular extension 20, which extension is removable for access tothe interior of the cylinder. This second end of the cylinder 10 issealed by a gland 22 that carries an O-ring 24 in sealing contact withthe cylinder wall and a second O-ring 25 in sealing contact with thepiston rod 14.

The tubular extension 20 houses the corresponding end of the tubularpiston rod 14 and is of ample length to accommodate the full range ofmovement of the piston rod. This tubular extension 20 is connected tothe xed structure of the reclining seat at a point towards the front ofthe seat, and for this purpose may be provided with a transverse sleeveinsert 26 to receive and journal a suitable connecting pin (not shown).The sleeve insert 26 is centrally bored, as shown, to vent the interiorof the tubular extension 20 to prevent compression of air therein bymovement of the piston rod 14.

The opposite end of the piston rod 14 is suitably adapted for pivotalconnection to the tiltable back rest of the chair at a point below thetilt axis. For this purpose, the piston rod 14 may extend through acentral bore 28 of a cross pin 29 for anchorage thereto by a pair ofnuts 30, and the two ends of the cross pin may be journaled in thecorresponding arms 31 of a U-shaped bracket 32. The two ends of thecross pin 29 function as trunnions and are held against an axialmovement by suitable spit retainer rings 33 on opposite sides of thebracket arms 31. The U-shaped bracket 32 is adapted to be xedly attachedto the tiltable back rest of the seat.

When the back rest of the chair is at its nearly vertical forwardposition, the described hydraulic structure is at its maximum extensionwith the piston 12 near the left end of the cylinder 1@ as viewed inFig. l. On the other hand, when the back rest is inclined backward toits limit position, the described hydraulic structure is contracted inlength with the piston 12 near the right end of the cylinder 1t). It isapparent that changes in degree of extension of the hydraulic structureinvolves ow of the hydraulic fluid between a hydraulic chamber 34 on theleft side of the piston and a hydraulic chamber 35 on the right side ofthe piston, and it is further apparent that the structure may beimmobilized with respect to extension and contraction by cutting olfiluid communication between these two hydraulic chambers. What may betermed a locking valve including a ball valve member 36 serves thispurpose.

It is usually desirable to provide an outer spring 37 to act incompression between the cylinder 10 and the piston rod 14 to tend toextend the hydraulic structure. In the construction shown, the spring 37is compressed between a flange 38 of the cylinder and an end wall 39 ofa cylindrical guard 40. The guard 40 is anchored to the piston rod 14 bytwo nuts 41 and 42. l

As best shown in Figure 2, the passageway for Huid communication betweenthe two hydraulic chambers 34 and 35 includes radial bores 44 in thetubular piston rod 14 on the left side of the piston 12, similar radialbores 45 on the right Iside of the piston and an axial passage 46through the piston 12. The axial passage 46 is formed by a valve seatmember 48 that is in the form of a threaded bushing. This valve seatmember has a circumferential flange 50 to conne a circumferential O-ring 52 and is formed with a diametrical end slot 54 to permit the valveseat member to be rotated by a screw driver.

The ball member 36 is-normally held Aseated in its closed position by acoiled valve spring 55 and a feature of the invention is the use of aoating ball guide 56 to transmit the spring pressure to the ball as asolely axial force. The ball guide 56 is a cup-shaped member having atransverse wall 58 in pressure abutment against the ball 36 and having acylindrical wall 60 that surrounds the ball with adesuate clearance toprevent any possible binding action on the ball. A clearance of .003"has been found to be adequate. The clearance between the ball guide 56and the surrounding wall of the piston rod 14 is adequate for a freesliding fit. Any nonaxial force component transmitted to the ball guide56 by the valve spring S5 merely tends to cant the ball guide to alimited extent without affecting the ball member 36. With the ballmember 36 subject only to purely axial force, the locking valve willmaintain its eiciency over a long service life.

The second end of the valve spring 5S seats against an over-rideadjusting screw 62 in the form of a plug threaded into the tubularpiston rod 14. The over-ride adjusting screw 62 is provided with anO-ring 64 and has a diametrical slot 65 at its outer end to permitrotational adjustment by means of a screw driver.

In the present embodiment of the invention, the locking valve isoperated by a push rod 70 of the configuration shown in Fig. 4. The pushrod 70 is formed with a tapered circumferential shoulder 72 and areduced end portion 74. The reduced end portion 74 of the push rodextends into the interior of the valve seat member 48 and may beadvanced against the ball member 36 to open the locking valve as shownin Fig. 5.

The interior of the tubular piston rod 14 in the region of the push rod70 serves as a reservoir 75 for a reserve portion of the hydraulic uid.The reservoir 75 has a movable end wall in the form of an auxiliarypiston 76, and what may be termed a reservoir spring 78 acts againstthis auxiliary piston to maintain the hydraulic fluid under a desirabledegree of pressure. Preferably a short guide sleeve 79 floats inside thespring 78 and keeps the spring from being compressed to a solid state.

As best shown in Fig. 3, the auxiliary piston 76 slidingly embraces thepush rod 7) and is provided with a circumferential Q-ring 89 for sealingcontact with the inner wall of the tubular piston rod 14. The auxiliarypiston 76 is also formed with a cylindrical end skirt 82 to confine anQ-ring S4 in sealing contact with the push rod 70. An annular followerfor seating the end of the reservoir spring 78 fits into the end skirt82 with a pressed t.

Since backward movement of the back rest of the reclining seat involvesrightward movement of the piston 12 as viewed in Fig. 1, it is apparentthat the locking valve functions in a positive manner to preventrearward tilt of the back rest regardless of the force exerted againstthe back rest by the seat occupant. On the other hand, return movementof the back rest towards its forward position involves leftward movementof the piston 12 as viewed in Fig. l.

A feature of the invention in this regard is that the back rest may berestored to its normal forward position manually without taking thetrouble to open the locking valve by means of the push rod 70. Thus, theback rest may be pushed forward manually, the pressure in the hydraulicchamber 34 being raised suiciently by the manual effort to cause theball member 36 to be unseated for fluid flow from the hydraulic chamber34 into the hydraulic chamber 35. Unfortunately, however, such apressure rise sulticient to override the locking valve is also sucientto compress the reservoir spring'78, with consequent displacement offluid from the hydraulic chamber 34 into the reservoir 75 instead ofthrough the locking valve into the hydraulic chamber 35. As heretoforestated, a feature ofthe invention is the provision of a check valve toprevent such a surge of hydraulic uid into the reservoir.-

As best shown in Figs. 3 and 4, the check valve for this purpose ofpreventing surge into the reservoir may be in the form of a floatingring or annular piston 86 carrying a circumferential O-ring 8S insealing contact with the surrounding wall of the tubular piston rod. Theinner diameter of the check valve member 86 is somewhat larger indiameter than the reduced end portion 74 of the push rod 70 that itsurrounds, there being adequate clearance for fluid flow from one sideof the check valve member to the other. In the event a pressure surgetends to displace hydraulic fluid into the reservoir 75, the check valvemember 86 is forced against the tapered shoulder 72 of the push rod 70and a tapered seat 90 formed in the check valve member makes sealingcontact with the tapered shoulder. It is desirable, however, to providea bypass for iiuid flow at the closed position of the check valve member86 to permit minor flow from the hydraulic chamber 34 into the reservoir75 to compensate for-thermal expansion and contraction of the uid in thesystem. Instead of forming such a bypass in the check valve memberitself, the bypass may be formed by cutting away a portion of thetapered shoulder 72 of the push rod 70, as indicated at 92 in Fig. 4.

With the locking Valve closed, thermal expansion of the hydraulic uidtrapped in the hydraulic chamber 35 results in slight leftwarddisplacement of the piston 12, as viewed in Figure l, and this pistondisplacement `together with thermal expansion of the hydraulic fluid inthe hydraulic chamber 34 causes uid displacement from the hydraulicchamber 34 into the reservoir 75 in opposition to the reservoir spring78. On the other hand, thermal contraction of the hydraulic iiuid in thesystem results in corresponding fluid flow from the reservoir 75 intothe hydraulic chamber 34 with slight rightward shift of the piston 12.

The reservoir spring 78 should have an effective force at least as greatas the effective force of the outer spring 37 for static balance betweenthe two springs. In other words the spring 78 should produce a fluidpressure at least equal to the varying back pressure created in thereservoir 75 and in the hydraulic chamber 34 by the spring 37.

The push rod 70 may be actuated in various ways in various practices ofthe invention. In this instance, a cam arrangement is provided to causethe push rod 70 to be shifted longitudinally in response to oscillationof a rotary operating member 94 (Figures 1, 6 and 7). As shown in Figure7, the operating member 94 carries an operating arm 95 that isadjustably iixed thereto by a l pair of cooperating nuts 96. The usualpush button on the reclining chair for opening operation of the lockingvalve may be operatively connected to the operating arm 95 in anysuitable manner, for example, by means of a cable as disclosed in thepreviously mentioned Armstrong patent.

The rotary operating member 94 is journaled in an externally threadedsleeve 98 that is threaded into the end of' the tubular piston rod 14,the sleeve extending beyond the end of the tubular piston rod and therotary operating member extending beyond the end of the sleeve. Thepreviously mentioned nuts 41 and 42 are threaded onto the sleeve 98 andas shown in Fig. 6, the nut 42 is tightened against the outer end of thetubular piston rod 14 to releasably tix the sleeve relative to thepiston rod. Thus, the two nuts 41 and 42 rnay be loosened to permitadjustment of the sleeve 98 as desired. The sleeve 98 serves, in effect,as an extension of the tubular piston rod and carries the cross pin 29for connection with. the tiltable back rest of the chair as heretoforedescribed.

The inner end of the sleeve 98 forms a cam 100 with a circumferentiallyextending camsurface. As best shown in Fig. 7, the cam has a valley 102and a sloping cam surface 104. Preferably, there are two diametricallyopposite valleys 102 and two diametrically opposite sloping shoulders104. The rotary operating member- 94 is` ,provided with a cam followerin theform of a cross pin which is in continuous contact with the cam100. Adjacent the cross pin 105,y the rotary operating member 94 isformed with a circumferential flange 106 and the inner end of the rotaryoperating member is bored to form a socket for the butt end of thepreviously mentioned push rod 70. The previously mentioned reservoirspring 78 seats against the circumferential ange 106 of the rotaryoperating member, thereby continuously pressing the follower or crosspin 105 against the cam 100 to cause the cross pin to seek the two camvalleys 102. It is to be further noted that the valve spring 55 alsoapplies pressure in the saine direction through the push rod 70 wheneverthe push rod is ladvanced against the resistance of the valve spring.The pressure of the cross pin 105 against the sloping shoulders 104ofthe cam tends to return the rotary operating member 94 and itsoperating arm 95 to their normal inoperative positions whenever theoperating push button on the reclining chair is relaxed.

The manner in which the invention serves its purpose may be readilyunderstood from the foregoing description. It is readily apparent thatthe two nuts 41 and 42 may be loosened to permit adjustment of thesleeve l9S at the factory to eliminate the need for any such adjustmentduring the installation of the device in a reclining chair. With the twonuts 41 and 42 loose, the sleeve 98 may be rotated with the cross pin105 in the'cam valleys 102 until the reduced end 74 of the push pin 70unseats the ball member 36. The sleeve 98 is then retracted slightly tomake sure that the push rod 70 is normally slightly retracted from theball 36 to avoid interfering with the normal seating of the ball.

Whenever depressions of the push button on the reclining chair swingsthe operating arm 95 to shift the cross pin 105 up the two sloping camshoulders 104, the consequent inward longitudinal shift ofthe rotaryoperating member 94 in opposition tothe reservoir spring 78 istransmitted to the push rod 70 to cause the ball member 36 to beunseated. With the locking valve held open in this manner, the back restof the reclining chair may be freely adjusted to -any desired angle ofinclination, with consequent tluid flow through the locking valve andthen the push button may be released to cause the locking valve to closefor immobilizing the back rest at the selected angle.

The locking valve prevents backward movement of the back rest in a`positive manner, but will open in response to pressure suicient tooverride'the valve spring 55 whenever substantial force is appliedmanually to the inclined back rest in a direction to restore thebackrest to its normal forward position. Whenever such overriding fluidpressure is created in the hydraulic chamber 34, the check valve 86functions in the manner heretofore described to keep the hydraulic fiuidfrom surging into the reservoir 75.

In some instances, where the mechanism of the reclining chair providesrelatively light operating force for opening the locking valve, thepressure of the reservoir spring 73 may be isolated from the rotaryoperating member 94 so that only the relatively light valve spring 55resi-sts the applied operating force'. Figs. 6 and 7 show how a spacermember 1-10 may be added for the purpose of isolating the pressure ofthe reservoir spring 78.

The spacer is in the form of a collar that -is slidingly mounted on therotary operating member 94 between the cross pin 105 andthecircumferential ange 106. The spacer collar 110 receives the springpressure from the circumferential ange 106 and transmits the pressure tothe cam 100, the spacer collar having a recess 112 to avoid pressingagainst the cross pin 105 and to permit freedom for movement of thecross pin along thesloping shoulders 104 of the cam. The two camshoulders '104 are each of approximately 90 extent circumferentially,but in all instances, the range of operating rotation of the rotaryoperating member 94 is substantially less than 90 and usually is lessthan 60.

My description in specific detail of the preferred embodiment of theinvention will suggest various changes, substitutions and otherdepartures from my disclosure Within the spirit and scope of theappended claims. 1 claim as my invention:

l. In a locking device of the character described having a cylinder, apiston assembly including a piston rod and a piston dividing thecylinder into two hydraulic chambers, a uidv passage in said pistonassembly for fluid `fiow between said chambers, and a normally closedlocking valve in said passage to control ilow therethrough, thecombination therewith of a mechanism `for opening said locking valve,said mechanism comprising: a push rod to operate the locking valve, saidpush rod being slidingly mounted inside said piston rod at a positionspaced inwardly from one end of the piston rod; a rotary operatingmember slidingly journaled in said one end of the piston rod coaxiallythereof; a cam element in said piston rod comprising an annular membersurrounding said push rod and shaped with a cam edge at one end; and aradial follower element in said piston rod for cooperation with said camedge to shift said push rod, one of said two elements being. stationaryrelative to the piston rod, the other of the two elements being a rotaryelement and being operatively connected to said rotary operating memberfor rotation therewith for cam action between said cam and said followerto shift said rotary operating member axially against said push rod toshift said push rod towards the locking valve.

2. A combination as set forth in claim l, in which said stationaryelement is adjustable to various rotary positions relative :to therotary element to vary the responsiveness of said push rod to rotationof said rotary operating member.

3. A combination as set forth in claim 1, in which said cam element isthe stationary element and is in the form of a threaded sleeve screwedinto said piston rod for rotary adjustment therein, said operatingmember extending through said sleeve.

4. A combination as set forth in claim 3, in which said sleeve extendsout of the end ofthe piston rod for convenienoe of manual adjustment;and which includes means also outside the piston rod to releasablyengage both the sleeve and the piston rod to immobilize said sleeverelative to the piston rod.

5. A combination as set forth in claim l, which includes an auxiliarypiston inside said piston rod and slidingly embracing said push rod toserve as a movable end wall of a hydraulic fluid reservoir; and in whicha coil spring surrounds said push rod, .one end of the spring pressingagainst said auxiliary piston to keep the hydraulic fluid underpressure, the other end of the spring exerting pressure against saidrotary element to hold the rotary element against the stationary elementand to resist operating rotation of the rotary element.

6. A combination as set forth in claim l, which includes: an auxiliarypiston inside said piston rod and slidingly embracing said push rod toserve as a movable end wall of a hydraulic fluid reservoir; a coilspring surrounding said push rod, one end of said spring pressingagainst said auxiliary piston to keep the hydraulic iluid underpressure, the other end of the spring being in the region of said rotaryelement; and a spacer collar receiving the pressure of the other end ofsaid spring and bridg- 8 ing the range of movement of said rotaryelement to keep the spring pressure away from the rotary element.

7. in a locking device of the character described having a cylinder, apiston assembly including a piston rod and a piston dividing thecylinder into two hydraulic chambers, a iiuid passage in said pistonassembly for iiuid ow between said chambers, and a locking valve in saidpassage to control flow therethrough, the combination therewith of amechanism for opening said locking valve, said mechanism comprising:spring means normally holding said locking valve closed; a push rod toopen said locking valve in opposition to said spring means, said pushrod being slidingly mounted inside said piston rod at a position spacedaway from one end of the piston rod; a `sleeve mounted in said one endof the piston rod, the inner edge of said sleeve forming a cam, saidsleeve being threaded into the piston rod for rotary adjustment of saidcam; means to releasably lock said sieeve at selected positions ofadjustment; and a rotary operating member having a radial follower incooperating contact with said cam edge whereby rotation of the operatingmember causes longitudinal displacement thereof for valve openingdisplacement of the push rod.

8. A combination as set forth in claim 7, which includes: an auxiliarypiston inside said piston rod and slidingly embracing said push rod todefine with said piston rod a reservoir for the hydraulic fluid; a coilspring inside the piston rod having one of its ends pressing againstsaid auxiliary piston to keep the hydraulic tiuid under pressure, theother end of said spring exerting pressure against said follower toresist valve-opening operation thereof.

9. In a locking device of the character described having a cylinder, apiston assembly including a hollow piston rod and a piston in saidcylinder carried by said piston rod and dividing the cylinder into twohydraulic chambers, and a fluid passage in said piston assembly forfiuid flow between said chambers, the combination therewith of means tocontrol iiow through said passage, said control means comprising: anannular valve seat in said passage; a valve member for cooperation with-said seat; a valve spring urging said valve member towards said seat;and a push rod slidingly mounted in said piston rod for longitudinaldisplacement through said valve seat to shift said valve member to openposition, said push rod being removable through one end of the pistonrod, said valve seat being threaded into said piston assembly and beingremovable for replacement through the same end of the piston rod.

l0. A combination as set forth in claim 9, in which said valve seat hasa diametrical slot for engagement by a screw driver.

ll. ln a locking device of the character described having a cylinder, apiston assembly including a piston rod and a piston in said cylinderdividing the cylinder into two hydraulic chambers and a fluid passage insaid piston assernbiy for iiuid flow between said chambers, thecombination therewith of means to control iiow through said passage,said control means comprising: an annular valve seat in said passage; avalve ball for cooperation with said seat; a valve spring urging saidball to closed position; a guide for said ball interposed between theball and the spring to receive the pressure of the spring and totransmit the pressure to the ball, said ball guide being slidinglymounted in said piston assembly in abutment with the ball and looselysurrounding the ball to keep the ball out of contact with surroundingstationary structure of the piston assembly; and means to unseat saidball in opposition to said spring, said unseating means including amember positioned to extend through the valve seat into contact with thevalve ball.

l2. in a locking device of the character described having a cylinder, apiston assembly including a tubular piston rod and a piston dividing thecylinder into two hydraulic chambers, a fluid passage in said pistonassembly for uid flow between said two chambers, a normally closedlocking valve in said passage to control ow therethrough, and means toopen said valve including a longitudinally movable push rod inside saidpiston rod, reservoir means inside said piston rod for containinghydraulic uid, said reservoir means including: an auxiliary pistonslidingly mounted inside said piston rod and slidingly embracing saidlongitudinally movable push rod to serve as an end Wall of thereservoir; a shoulder on said longitudinally movable rod; an annularcheck valve member surroundingl said longitudinally movable rod insliding sealing contact with the inner wall surface of the piston rodbetween said auxiliary piston and said locking valve with clearancebetween the annular check valve member and the longitudinally movablepush rod for iluid ow into and out of Athe reservoir, said check valvemember being movable by uid pressure to a closed position against saidshoulder to prevent a surge of pressure against the auxiliary piston;and a bypass for fluid ow through said check valve member at its closedposition.

13. A combination as set forth in claim 12, in which said shoulder is anannular shoulder on said longitudinally movable push rod for abutmentagainst said check valve member to restrict ow through the check valvemember.

14. A combination as set forth in claim 13, in which said shoulder isrecessed to form said bypass.

References Cited in the le of this patent UNITED STATES PATENTS

